The present invention generally relates to power transmission systems. More particularly, this invention relates to a powersplit transmission for a vehicle, in which the powersplit transmission may be operated in a hydrostatic power transmission mode or a blended hydrostatic and mechanical power transmission mode.
Vehicles that incorporate the powersplit transmission, such as earth moving machinery, industrial equipment, and others may be operated in the hydrostatic power transmission mode or the blended hydrostatic and mechanical power transmission mode. In the hydrostatic power transmission mode, a speed of the vehicle or a motion of a hydraulically operated attachment coupled to the vehicle may be precisely controlled. Such a mode of operation is particularly useful when loading and unloading the vehicle, performing work with the hydraulically operated attachment, or maneuvering the vehicle in constrained areas, for example. In the blended hydrostatic and mechanical power transmission mode, a portion of an output of a prime mover of the vehicle bypasses a hydrostatic portion of the powersplit transmission. Such a mode of operation is useful to increase an efficiency of the vehicle and increase a range of operating speeds of the vehicle, for example.
An operator of the vehicle typically desires to change from the hydrostatic power transmission mode to the blended hydrostatic and mechanical power transmission mode. Such a process is usually performed while the vehicle is performing work, such as accelerating the vehicle. When the powersplit transmission changes from the hydrostatic power transmission mode to the blended hydrostatic and mechanical power transmission mode, the vehicle typically experience a torque interruption.
It would be advantageous to develop a method for shifting a powersplit transmission between modes of operation that minimizes torque interruption, increases a fuel efficiency of a vehicle, and increases a range of operating speeds of the vehicle the powersplit transmission is incorporated in.